The phosphoinositide 3-kinases (PI3Ks) belong to a large family of lipid signaling kinases that phosphorylate phosphoinositides at the D3 position of the inositol ring (Cantley, Science, 2002, 296(5573):1655-7). PI3Ks are divided into three classes (class I, II, and III) according to their structure, regulation and substrate specificity. Class I PI3Ks, which include PI3Kα, PI3Kβ, PI3Kγ, and PI3Kδ, are a family of dual specificity lipid and protein kinases that catalyze the phosphorylation of phosphatidylinosito-4,5-bisphosphate (PIP2) giving rise to phosphatidylinosito-3,4,5-trisphosphate (PIP3). PIP3 functions as a second messenger that controls a number of cellular processes, including growth, survival, adhesion and migration. All four class I PI3K isoforms exist as heterodimers composed of a catalytic subunit (p110) and a tightly associated regulatory subunit that controls their expression, activation, and subcellular localization. PI3Kα, PI3Kβ, and PI3Kδ associate with a regulatory subunit known as p85 and are activated by growth factors and cytokines through a tyrosine kinase-dependent mechanism (Jimenez, et al., J Biol Chem., 2002, 277(44):41556-62) whereas PI3Kγ associates with two regulatory subunits (p101 and p84) and its activation is driven by the activation of G-protein-coupled receptors (Brock, et al., J Cell Biol., 2003, 160(1):89-99). PI3Kα and PI3Kβ are ubiquitously expressed. In contrast, PI3Kγ and PI3Kδ are predominantly expressed in leukocytes (Vanhaesebroeck, et al., Trends Biochem Sci., 2005, 30(4):194-204).
The differential tissue distribution of the PI3K isoforms factors in their distinct biological functions. Genetic ablation of either PI3Kα or PI3Kβ results in embryonic lethality, indicating that PI3Kα and PI3Kβ have essential and non-redundant functions, at least during development (Vanhaesebroeck, et al., 2005). In contrast, mice which lack PI3Kγ and PI3Kδ are viable, fertile and have a normal life span although they show an altered immune system. PI3Kγ deficiency leads to impaired recruitment of macrophages and neutrophils to sites of inflammation as well as impaired T cell activation (Sasaki, et al., Science, 2000, 287(5455):1040-6). PI3Kδ-mutant mice have specific defects in B cell signaling that lead to impaired B cell development and reduced antibody responses after antigen stimulation (Clayton, et al., J. Exp. Med. 2002, 196(6):753-63; Jou, et al., Mol. Cell Biol. 2002, 22(24):8580-91; Okkenhaug, et al., Science, 2002, 297(5583):1031-4).
The phenotypes of the PI3Kγ and PI3Kδ-mutant mice suggest that these enzymes may play a role in inflammation and other immune-based diseases and this is borne out in preclinical models. PI3Kγ-mutant mice are largely protected from disease in mouse models of rheumatoid arthritis (RA) and asthma (Camps, et al., Nat Med. 2005, 11(9):936-43; Thomas, et al., Eur. J. Immunol., 2005, 35(4):1283-91). In addition, treatment of wild-type mice with a selective inhibitor of PI3Kγ was shown to reduce glomerulonephritis and prolong survival in the MRL-lpr model of systemic lupus nephritis (SLE) and to suppress joint inflammation and damage in models of RA (Barber, et al., Nat Med. 2005, 11(9):933-5; Camps, et al., 2005). Similarly, both PI3Kδ-mutant mice and wild-type mice treated with a selective inhibitor of PI3Kδ have been shown to have attenuated allergic airway inflammation and hyper-responsiveness in a mouse model of asthma (Ali, et al., Nature. 2004, 431(7011):1007-11; Lee, et al., FASEB J. 2006, 20(3):455-65) and to have attenuated disease in a model of RA (Randis, et al., Eur. J. Immunol., 2008, 38(5):1215-24).
In addition to their potential role in inflammatory diseases, all four class I PI3K isoforms may play a role in cancer. The gene encoding p110α is mutated frequently in common cancers, including breast, prostate, colon and endometrial (Samuels, et al., Science, 2004, 304(5670):554; Samuels, et al., Curr. Opin. Oncol. 2006, 18(1):77-82). Eighty percent of these mutations are represented by one of three amino acid substitutions in the helical or kinase domains of the enzyme and lead to a significant upregulation of kinase activity resulting in oncogenic transformation in cell culture and in animal models (Kang, et al., Proc. Natl. Acad. Sci. U.S.A. 2005, 102(3):802-7; Bader, et al., Proc. Natl. Acad. Sci. U.S.A. 2006, 103(5):1475-9). No such mutations have been identified in the other PI3K isoforms although there is evidence that they can contribute to the development and progression of malignancies. Consistent overexpression of PI3Kδ is observed in acute myeloblastic leukemia (Sujobert, et al., Blood, 2005, 106(3):1063-6) and inhibitors of PI3Kδ can prevent the growth of leukemic cells (Billottet, et al., Oncogene. 2006, 25(50):6648-59). Elevated expression of PI3Kγ is seen in chronic myeloid leukemia (Hickey, et al., J. Biol. Chem. 2006, 281(5):2441-50). Alterations in expression of PI3Kβ, PI3Kγ and PI3Kδ have also been observed in cancers of the brain, colon and bladder (Benistant, et al., Oncogene, 2000, 19(44):5083-90; Mizoguchi, et al., Brain Pathol. 2004, 14(4):372-7; Knobbe, et al., Neuropathol. Appl. Neurobiol. 2005, 31(5):486-90). Further, these isoforms have all been shown to be oncogenic in cell culture (Kang, et al., 2006).
Thus, new or improved agents which inhibit kinases such as PI3K are continually needed for developing new and more effective pharmaceuticals that are aimed at augmentation or suppression of the immune and inflammatory pathways (such as immunosuppressive agents for organ transplants), as well as agents for the prevention and treatment of autoimmune diseases (e.g., multiple sclerosis, rheumatoid arthritis, asthma, type I diabetes, inflammatory bowel disease, Crohn's disease, autoimmune thyroid disorders, Alzheimer's disease, nephritis), diseases involving a hyperactive inflammatory response (e.g., eczema), allergies, lung diseases, cancer (e.g., prostate, breast, leukemia, multiple myeloma), and some immune reactions (e.g., skin rash or contact dermatitis or diarrhea) caused by other therapeutics. The compounds, compositions, and methods described herein are directed toward these needs and other ends.